Silk keeps fruit fresh

Mark Waghorn

Fruit and vegetable could become cheaper after scientists discovered that a chemical in silk keeps them fresh and juicy for more than a week.

A study has found spraying delicate produce with the chemical reduces wastage without the need for refrigeration.

The odourless, ultra thin solution is virtually invisible and offers an alternative for preserving delicate foods.

Experiments on strawberries and bananas found it prolonged room temperature freshness and firmness, preventing decay without affecting texture.

The naturally derived material and water based manufacturing process could even help address world famine.

Half of the world’s fruit and vegetable crops are lost during the food supply chain, mainly because of premature deterioration of the perishable foods, according to UN research.

The study published in Scientific Reports said silk’s unique crystalline structure makes it one of nature’s toughest materials.

And its insoluble protein fibroin has a remarkable ability to stabilise and protect other materials while being fully bio-compatible and degradable.

Freshly picked strawberries were dipped in a solution of one percent fibroin up to four times. The fruits were then treated with water vapour to create varying amounts of chemical structures called beta sheets.

The longer the exposure, the more beta sheets and the stronger the fibroin coating became. It measured 27 to 35 microns thick, up to four times thinner than the diameter of a human hair.

The strawberries were then stored at room temperature. Uncoated berries were compared over time with those dipped in varying numbers of coats of silk.

At seven days, the berries coated with the higher beta sheet silk were still juicy and firm while the uncoated berries were dehydrated and discoloured.

Professor Fiorenzo Omenetto, of Tufts University, Massachusetts, said: “The beta sheet content of the edible silk fibroin coatings made the strawberries less permeable to carbon dioxide and oxygen. We saw a statistically significant delay in the decay of the fruit.”

Similar experiments were performed on bananas, which, unlike strawberries, are able to ripen after they are harvested.

The silk coating decreased the bananas’ ripening rate compared with uncoated controls and added firmness by preventing softening of the peel.

Taste was not studied, although the researchers hope to carry out more work to make the coating even better.

Added Dr Benedetto Marelli, now at the Massachusetts Institute of Technology: “Various therapeutic agents could be easily added to the water-based silk solution used for the coatings, so we could potentially both preserve and add therapeutic function to consumable goods without the need for complex chemistries.”

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